1. Field of the Invention
The present invention relates to a flexible substrate one end of which is connected, for example, to a conductor pattern on a printed circuit board and the other end of which is connected to a connector mounted to this printed circuit board or to a conductor pattern of another printed circuit board. In the present invention, an improvement is achieved in terms of the strength with which the flexible substrate is connected to the printed circuit board by soldering.
2. Description of the Related Art
With reference to FIGS. 9 through 11, a conventional manner in which a printed circuit board and a flexible substrate are connected together will be described. FIG. 9 is a plan view; FIG. 10 is a sectional view taken along the line X--X of FIG. 9; and FIG. 10 is a detailed view of the portion B of FIG. 10.
On a printed circuit board 41, a plurality of conductor patterns 42 are arranged side by side and extend from a circuit formed at a position (not shown) on the printed circuit board 41 to the vicinity of an end portion 41a. On a flexible substrate 43 to be connected to this printed circuit board 41, a plurality of conductor patterns 44 are arranged side by side and extend to the vicinity of an end portion 44a.
Each of these conductor patterns 42 and 44 has a fixed width, with its side ends being linear. The pitch of the conductor patterns 44 of the flexible substrate 43 is the same as the pitch of the conductor patterns 42 of the printed circuit board 41. Further, the width Wb of the conductor patterns 44 of the flexible substrate 43 is smaller than the width Wa of the conductor patterns 42 of the printed circuit board 41.
Cream solder is applied to the conductor patterns 42 of the printed circuit board 41. As shown in FIG. 10, the plurality of conductor patterns 44 of the flexible substrate 43 are opposed to the plurality of conductor patterns 42 of the printed circuit board 41 such that each conductor pattern 44 is situated at a position substantially corresponding to the center of the associated conductor pattern 42. The printed circuit board 41 and the flexible substrate 43 are stacked together and connected to each other by an appropriate method using a reflow furnace or the like.
Solder does not easily adhere to the opposed contact surfaces of the conductor patterns 42 of the printed circuit board 41 and the conductor patterns 44 of the flexible substrate 43. Generally speaking, as shown in FIG. 11, the adhesion of the solder is effected such that the solder extends from the side ends 44a of the conductor patterns 44 of the flexible substrate 43, which have a relatively small width, over the upper surfaces of the conductor patterns 42 of the printed circuit board 41 which are outside these side ends 44a.
In the above construction, however, the side ends 44a of the conductor patterns 44 of the flexible substrate 43 are linear, and the thickness of the conductor patterns 44 of the flexible substrate 43 is small, so that the solder fillets 45 connecting the conductor patterns 42 of the printed circuit board 41 with the side ends 44a of the conductor patterns 44 are small, as shown in FIG. 11. Further, the connecting distance X over which the solder fillets 45, extending from the side ends 44a of the conductor patterns 44 of the flexible substrate 43, are connected with the conductor patterns 42 of the printed circuit board 41 is rather small.
As a result, the strength with which the conductor patterns 42 of the printed circuit board 41 are connected to the conductor patterns 44 of the flexible substrate 43 is rather low, so that the printed circuit board 41 and the flexible substrate 43 are liable to be separated from each other.